Industrial wastewater can contain many different kinds of impurities, including, for example, greases, oils, metals and other inorganic compounds, solid particulate matter (dirt), organic compounds, etc. It is desirable to remove as much of these impurities as possible. Further, government regulations require removal of impurities, particularly some metals, and such regulations have become increasingly stringent. Known techniques for removal of metals from wastewater include ultrafiltration, reverse osmosis, and ion exchange techniques. These techniques are all relatively expensive and generally produce a concentrated waste which requires further handling or treatment.
Physical-chemical treatment processes are also commonly used to purify wastewater. In these systems, hydroxide or sulfide precipitation is used. A lime slurry, caustic soda, ferrous or other soluble sulfide salts precipitates a wide range of dissolved impurities and induces aggregation and precipitation of particulate materials and specifically metal ions. In these systems, metal salts (typically iron), coagulating chemicals and polymers are often used to encourage the colloidal metal hydroxide or sulfide particulate to coagulate and flocculate. The resulting flocs with their accumulated contaminants are then removed either by sedimentation or filtration. However, such known techniques have limitations. Specifically, physical-chemical processes are susceptible to organic materials in the wastewater impurities. That is, the organic materials can interfere with precipitation and removal of metals, reducing the efficacy of the system. Moreover, systems have difficulty meeting the new, more stringent federal requirements. Additionally, hydroxide precipitates will not precipitate complexed metals. Complexed metals have a tendency to remain bound in solution bound rather than form precipitates and settle out. These metals have reacted with complexing agents such as EDTA, ammonia, etc. Furthermore, while sulfide precipitation provides greater metal removal efficiency than hydroxide precipitation, it is relatively expensive and it produces toxic hydrogen sulfide gas if the pH drops below 8. As a result sulfide precipitation is rarely used. It would be highly desirable to have a low cost and highly effective system for removal of metals and other impurities out of industrial wastewater.
Animal bone charcoal (Bone Black, Bone Char) is the product of the dry distillation of animal bones. Raw materials used for bone charcoal production have heretofore been exclusively of bovine origin. Bones from other animals, such as pigs, goats, horses, etc., have proven to be unsuitable for making bone char, as they are too brittle and do not have the porosity of cattle bones. Bone charcoal has been shown to be effective in reducing the levels of many contaminants in water. For example, U.S. Pat. No. 4,902,427 to Szczepanik describes use of a filter cartridge for removing heavy metals and organic contaminants from water. The cattle bone char used has a particulate size of no larger than 200 mesh. (The larger the mesh, the smaller the diameter of the bone char.) In many applications for treatment and removal of impurities from industrial wastewater such known commercially available bone char is too expensive to use for larger flow rates and higher metals loading.
Such known cattle bone char of small particulate size is not practical for industrial wastewater applications using pressurized vessels. This is because of the long reaction time required, the tendency of the bone char to compact, forming a unreactive, rock-like material, and the tendency of the bone char to blow out of the vessel when pressurized.
U.S. Pat. No. 6,217,775 to Conca et al describes treatment of metal-contaminated leachates utilizing fish bones and fish hard parts. In such systems, fish bones and fish hard parts have “amounts of organics associated therewith”. For many water treatment applications, such organics are undesirable and in fact counterproductive to treatment objectives.